The field of the invention is that of surge protection systems and more particularly to protectors for high voltage and current transients that may occur on telephone tip or ring lines.
Solid state surge protection systems conventionally employ a surge protection device having a semiconducting element disposed between a pair of electrodes. This element is arranged in the circuit to selectively conduct electrical energy between the tip line and common, the ring line and common and, if desired, between the tip line and the ring line. For example, in the event the telephone circuit experiences an electrical surge as a result of lightning or A.C. line cross or the like in the circuit, the system is designed to shunt current from and thereby to protect telecommunication equipment connected in the circuit from damage due to the surge condition. On occasion, the circuit may experience an electrical surge which results in destruction of the semiconducting element so that the circuit components and telecommunication equipment would not thereafter be protected against subsequent occurring electrical surge conditions. Accordingly, the conventional surge protection systems typically incorporate means designed to move the electrodes into electrical engagement with each other following destruction of the semiconducting element, thereby to maintain a short circuit condition between the electrodes to protect the circuit components and telecommunication equipment coupled to the circuit against subsequently occurring transient surge conditions until such time as the semiconducting element is replaced. For example, the device electrodes in a typical system are resiliently engaged between spring loaded electrical contact arms or the like to be biased together by the spring contact arm loading in the event the semiconducting element is destroyed by the noted surge conditions. Frequently, however, difficultly is encountered in establishing and maintaining the desired short circuit condition between the electrodes following destruction of the semiconducting element.
In copending application, Ser. No. 07/720,980, now U.S. Pat. No. 5,224,008, an improved surge protection device is described and claimed comprising a semiconducting element having first and second electrodes disposed in electrically conductive relation with respective opposite sides of the element and the element is normally operable to selectively conduct electrical energy between the electrodes to provide a first level of surge protection for the circuit. The element becomes conductive, for example, on occurrence of selected surge voltage in the circuit due to lightning or the like for connecting the circuit to ground to protect the circuit and circuit components from the voltage surge. When the surge condition has passed, the semiconducting element returns to its non-conducting condition permitting resumption of normal circuit operation. In the event the device is destroyed as a result of being subjected to a greater electrical surge exceeding the first level of surge as described above, the electrodes are adapted to contact each other to maintain a short circuit condition to thereby provide a second level of surge protection. A first one of the electrodes is disposed in electrical engagement with a limited portion of one side of the semiconducting element to facilitate establishment and maintenance of the desired short circuit condition between the electrodes in the event of element destruction. The first electrode comprises a disc part and post of lesser cross sectional size than the disc part. A distal end of the post part of the first electrode is secured in electrically conductive relation to the selected limited portion of the said one side of the element whereby as destruction of the semiconducting element occurs along a critical energy condition path, the post part of the electrode passes through the element along that path to be electrically engaged in short circuit condition with the second electrode for providing the second level of surge protection. While this protective device is effective it would be desirable to provide a device which is particularly suitable for mounting on a circuit board.